This invention relates to a system and method for providing uniform illumination of items, such as electronic components for purposes of vision system component image recognition and inspection.
With regard to electronic components, various methods of illumination have been utilized in order to illuminate all of the features of the components, as it is necessary that the components be adequately illuminated so that automated machine vision systems can operate for purposes of component image recognition and also vision system component inspection, where a camera, in association with sophisticated machine vision software, obtains image information concerning the components, and the machine vision software performs any number of well known analyses of the image information. For example, the image information is analyzed to determine whether a component is present, for component identification and inspection, and for determining location information concerning the component in order to obtain accurate placement of the component on a printed circuit board. Types of features to be illuminated include leads which extend out or away from the component body in any direction, spherical bumps, outer perimeter features of the components, etc.
Prior art methods of illumination include mounting light sources on all four sides of a component to provide 45xc2x0 angle of incidence illumination of the component, providing light to all sides of the component.
High angle illumination (high angle with respect to the optical axis) is often required to illuminate certain kinds of features of components, such as spherical bumps. One way in the prior art of accomplishing such high angle illumination is to provide lighting boards on all four sides of the component, where the lighting boards are tipped at approximately 5xc2x0 from the body plane of the component. This, in essence, provides a ring of light sources surrounding the component.
These prior art methods have a number of disadvantages, a significant one being that light sources must be provided on all four sides of the components. This presents a problem where there are a series of placement spindles next to one another, each spindle holding an individual component to be illuminated, and it is not possible to position illumination sources between each placement spindle.
The present invention relates to a method of providing compound angle illumination on a first side of an item, such as an electronic component and providing compound angle illumination on a second side of the component. An aspect of the method of the present invention also comprises tilting vertically the sources for the component illumination.
The present invention also relates to an apparatus that provides compound angle illumination on a first side of an item, such as an electronic component and on a second side of the electronic component. A first illumination assembly provides the illumination of the first side of the component and a second illumination assembly provides the illumination for the second side of the component. Substantially uniform illumination of the component or features of the component within the field of view of a camera is obtained. In one aspect of the invention, the light sources in the illumination assemblies are light emitting diodes and a refracting prism is utilized to refract the light from the LED""s at angles that result in criss-cross illumination of the component.